Helical rods, amphiphilic

Fig. 18 Schematic illustration of the preparation and photoresponsive behavior of the polypeptide XXIII, consisting oftwo amphiphilic helical rods linked by an azobenzene unit, a) Selective saponification of COOCH3 side...

The compound XXIII, consisting of two amphiphilic helical rods linked by an azobenzene moiety, was found to form micelles and ordered aggregates in aqueous solution in the dark, when the azo moiety is in the trans configuration. Photoisomerization of the azo linkage into the cis configuration, and the consequent bending in the structure of the molecules, induced disaggregation and disruption of the micelles.1118,1191... 

Hierarchical Higher Organization - From Bilayers to Fibers and Rods Amphiphile assembly sometimes results in higher order supramolecular assemblies. Fibrous structures and helical ribbons with molecular dimensions are formed spontaneously. 

A unique but widely studied polymeric LB system are the polyglutamates or hairy rod polymers. These polymers have a hydrophilic rod of helical polyglutamate with hydrophobic alkyl side chains. Their rigidity and amphiphilic-ity imparts order (lyotropic and thermotropic) in LB films and they take on a F-type stmcture such as that illustrated in Fig. XV-16 [182]. These LB films are useful for waveguides, photoresists, and chemical sensors. LB films of these polymers are very thermally stable, as was indicated by the lack of interdiffusion up to 414 K shown by neutron reflectivity of alternating hydrogenated and deuterated layers [183]. AFM measurements have shown that these films take on different stmctures if directly deposited onto silicon or onto LB films of cadmium arachidate [184]. 

It is apparent that the solubilization of amphiphilic molecules with chiral head groups produces aggregates such as braided fibers, helices, ribbons, rods, or tubules. When these organizations are sufficiently extended, they start to get entangled and develop the ability to entrap solvent molecules in the resulting reticulum. Many such instances eventually lead to the formation of gels. This phe-... 

---